NASA's Juno spacecraft is getting ready to launch toward the biggest planet in the solar system.

Juno is scheduled to take off between Aug. 5 and 26 on its five-year journey to Jupiter.

"It holds a lot of key secrets on how we formed the solar system," said Scott Bolton, the principal investigator of the mission, at a NASA news conference Wednesday.

Earlier in the morning, the solar-powered, hydrazine-propelled spacecraft was secured to the top of its rocket on a launch pad at Cape Canaveral, Fla.

Bolton said the spacecraft will cartwheel through space before it enters a close polar orbit around Jupiter in 2016. Juno will duck underneath Jupiter's hazardous radiation belt and circle just 5,000 kilometres above its clouds.

Juno has been carefully designed to protect its instruments from the violent radiation, Bolton said.

"We're basically an armoured tank going into Jupiter."

Some of the main goals of the mission are to:

Measure the amount of water in Jupiter's atmosphere, which will differ depending on how it formed.

Map its magnetic and gravity fields.

Probe deep into its atmosphere in an effort to find out whether it has a core of heavy elements like the Earth, or whether it is made of gas all the way through.

Examine the spectacular aurora at Jupiter's poles for comparison to that of other planets such as Earth's.

Juno will orbit far closer to Jupiter than the last visiting spacecraft, Galileo, which plunged to destruction into Jupiter's atmosphere in 2003. That means Juno will be able to get far better measurements of the planet's interior.